Ultraviolet light-emitting devices and methods

ABSTRACT

In various embodiments, an illumination device features an ultraviolet (UV) light-emitting device at least partially surrounded by an encapsulant. A barrier layer is disposed between the light-emitting device and the encapsulant and is configured to substantially prevent UV light emitted by the light-emitting device from entering the encapsulant.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/044,577, filed Feb. 16, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/679,655, filed Apr. 6, 2015, which claims thebenefit of and priority to U.S. Provisional Patent Application No.61/976,064, filed Apr. 7, 2014, the entire disclosure of each of whichis hereby incorporated herein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates to light emittersemitting ultraviolet (UV) radiation.

BACKGROUND

Light-emitting diodes (LEDs) are increasingly utilized in a variety ofdifferent lighting applications due to their lower energy consumption,longer lifetime, high physical robustness, small size, and fastswitching times. FIG. 1 depicts a conventional LED package 100, in whichan LED chip 105 is electrically and physically connected to a submount110 on a surface-mount device (SMD) package 115. Wires 120 electricallyconnect submount contacts to contact pads 125 on the SMD package 115,and a plastic lens 130 is placed over the LED chip 105 to focus thelight therefrom. As shown, a transparent liquid- or gel-based “glob top”encapsulant 135 is then disposed over all of the components within theSMD package 115 and cured to form a semi-rigid protective coating thatis also transparent to light emitted by the LED chip 105. Theencapsulant 135 typically has a lens-like shape to facilitate lightemission from the packaged LED chip 105. LED package 100 also mayfeature one or more electrical contacts 140 that electrically connectthe LED chip 105 to the submount 110, as well as an underfill 145. Asshown, the underfill 145 may be disposed between the LED chip 105 andthe submount 110 and provide mechanical support to the LED chip betweenthe electrical contacts 140.

UV LEDs have shown great promise for applications such as medicaltherapy, sensors and instrumentation, and fluid sterilization.Unfortunately, the above-described conventional packaging is frequentlyunsuitable for UV LEDs, which may emit light having wavelengths lessthan 320 nm, less than 265 nm, or even less than 200 nm. As shown inFIG. 1, when the LED chip is a UV LED, the highly energetic UV lightleads to deterioration and even formation of cracks 150 within thetransparent encapsulant. Such cracking may lead to distortions or breaksin the bonding wires 120 or failure of the LED package 100 due tomoisture introduced from the outside environment along the cracks 150.In addition, the UV radiation from UV LEDs can cause deterioration andeven failure of the plastic lenses 130 that are typically utilized atopother (e.g., visible-light-emitting) LEDs. In view of these issues,there is a need for improved packaging schemes for UV LEDs that enablehigh reliability, mechanical robustness, and long lifetime for thepackaged devices.

SUMMARY

In accordance with various embodiments of the present invention,high-reliability packages for UV LED chips include rigid lensesresistant to UV damage or deterioration in combination with a barrierlayer between light-emitting portions of the LED chip and anytransparent encapsulant utilized to encase the LED chip within thepackage. The barrier layer substantially prevents transmission of UVlight through the majority of such encapsulant, thereby preventingdeterioration and cracking (or other mechanical failure) thereof. Invarious embodiments of the invention, the barrier layer includes orconsists essentially of a portion of the encapsulant itself that isadjacent to the LED chip and opaque to the UV light emitted by the LEDchip. (In such embodiments, the remaining portion of the encapsulantfarther away from the LED chip may also be UV-opaque or transparent, asthis more distant encapsulant will typically not transmit the emitted UVlight.) As utilized herein, an “opaque” material substantially does nottransmit light of a particular wavelength or wavelength range (e.g., UVlight), and instead is reflective and/or strongly absorptive (e.g., overa small thickness) to light of the particular wavelength or wavelengthrange. In other embodiments of the invention, the barrier layer includesor consists essentially of a solid opaque shield disposed between theLED chip and the encapsulant, which may itself therefore be transparentor opaque to UV light. For example, the shield may be composed of ametal that is substantially reflective to UV light such as aluminum. Inthis manner, embodiments of the invention include packaged UV LEDshaving long lifetimes, high output power, and high reliability.

Moreover, various embodiments of the present invention ameliorate orprevent output degradation and/or lens detachment in packaged UV LEDs.In various embodiments, a force is applied between the LED chip and alens (e.g., a rigid lens) thereover in order to maintain contacttherebetween during thermal curing of the encapsulant material and/orduring UV emission (e.g., during operation and/or during burn-inprocesses in manufacturing). For example, the force may be a downwardforce applied to the lens toward the LED chip, an upward force appliedto the LED chip toward the lens, or a combination of both. The force mayadvantageously suppress or substantially prevent formation of bubbleswithin and/or at a thin layer of an interface material that is disposedbetween the LED chip and the lens. Such bubbles may be due, at least inpart, to, e.g., gas generated by decomposition of the interface materialduring curing and/or during UV emission while the LED is in operation.For example, application of heat to an interface material including orconsisting essentially of silicone may result in the formation ofbubbles of formaldehyde gas. Furthermore, while the LED is in operation,the emitted UV light may induce a photochemical reaction that takesplace in the interface material, and this reaction may result indecomposition of silicone that may result in the formation of bubbleswithin the interface material. The presence of the bubbles maydeleteriously impact the UV transparency of the interface material, and,if large enough, may result in at least partial detachment of the lensfrom the LED chip. The force, which may have a magnitude of, e.g.,between approximately 0.05 Newtons and approximately 10 Newtons, may beapplied by a portion of the encapsulant itself that vertically overlapsthe lens. When the encapsulant is cured, by e.g., application of heat,at least a portion of the encapsulant may thermally contract (due to,e.g., heat-induced volumetric shrinkage) and thereby apply thebubble-preventing force to the lens. For example, the encapsulant mayinclude, consist essentially of, or consist of a “heat-contractivematerial,” i.e., a material that experiences volumetric contraction uponapplication of heat. The volumetric contraction typically remains, atleast in part, after heating is complete (i.e., the original volume ofthe heat-contractile material is not recovered, at least not entirely,after the heating is finished). The heat-contractive material mayinclude, consist essentially of, or consist of, for example, a resin,e.g., a resin of polytetrafluoroethylene (PTFE), polyetheretherketone(PEEK), a fluoropolymer such as a perfluoroalkoxy alkane (PFA), and/orepoxy. In various embodiments, epoxy resin may be utilized for itsadvantageous moisture-blocking properties. At least in part becauseheat-contractive materials in accordance with embodiments of the presentinvention are elastic, and retain at least a portion of their elasticityafter volumetric contraction, at least a portion of the force appliedthereby during curing is retained even after curing (and in the absenceof applied heat). The force may continue to be applied by theheat-contractive material for a period of at least 10,000 hours, or evenat least 50,000 hours, and/or for a time period substantially equal toor exceeding the expected lifetime of one or more other components(e.g., the LED chip) of packaged UV LEDs in accordance with embodimentsof the present invention.

In an aspect, embodiments of the invention feature an illuminationdevice that includes or consists essentially of a light-emitting device,a package, an encapsulant, and a barrier layer. The light-emittingdevice is configured to emit ultraviolet (UV) light and may have atleast two spaced-apart contacts. At least a portion of the package maybe disposed beneath the light-emitting device. The contacts of thelight-emitting device are electrically connected to the package. Thelight-emitting device may be mechanically attached to a portion of thepackage. The encapsulant may be disposed on the package. The encapsulantat least partially surrounds the light-emitting device. The barrierlayer is disposed between the light-emitting device and the encapsulant.The barrier layer is configured (e.g., sized and/or shaped and/orpositioned) to substantially prevent UV light emitted by thelight-emitting device from entering the encapsulant.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The barrier layer may include, consistessentially of, or consist of a second encapsulant disposed adjacent tothe light-emitting device. The second encapsulant may be opaque to UVlight emitted by the light-emitting device. The encapsulant may besubstantially transparent to UV light emitted by the light-emittingdevice. The encapsulant may be opaque to UV light emitted by thelight-emitting device. The encapsulant and the second encapsulant mayinclude, consist essentially of, or consist of the same material. Apenetration length of UV light (e.g., the UV light emitted by thelight-emitting device and/or UV light having a wavelength rangepartially or fully overlapping with that of the UV light emitted by thelight-emitting device) within the second encapsulant may be less than 25μm, or even less than 10 μm. A penetration length of UV light within theencapsulant may be 100 μm or more (and may even be longer than adimension, e.g., width, radius, etc., of the encapsulant).

The barrier layer may include, consist essentially of, or consist of amaterial reflective to UV light emitted by the light-emitting device.The barrier layer may include, consist essentially of, or consist ofaluminum. At least a portion of the encapsulant may be substantiallytransparent to UV light emitted by the light-emitting device. At least aportion of the encapsulant may be substantially opaque to UV lightemitted by the light-emitting device. The UV light emitted by thelight-emitting device may have a wavelength of 265 nm or less, or even200 nm or less (and may have a wavelength of 10 nm or more). The packagemay include or consist essentially of a submount and asurface-mount-device (SMD) package. The contacts of the light-emittingdevice may be electrically and mechanically connected to the submount.The submount may be disposed above the SMD package and/or may beelectrically connected to the SMD package. The submount may beelectrically connected to the SMD package via one or more wire bonds.

A rigid inorganic lens may be disposed above the light-emitting deviceand may at least partially protrude from the encapsulant. The lens mayinclude, consist essentially of, or consist of quartz, fused silica,and/or sapphire. A top surface of the encapsulant (e.g., the top surfaceof the encapsulant adjoining and/or in contact with the lens) may bedisposed above a bottom surface of the lens by at least 0.05 mm. Atleast a portion of the encapsulant may apply a downward force on thelens toward the light-emitting device. The magnitude of the downwardforce may be greater than 0.1 N. A thin interface material (e.g., a gel,resin, cured or at least partially uncured polymer, or liquid) may bedisposed between the lens and the light-emitting device. The interfacematerial may have a thickness less than 5 μm. The interface material mayinclude, consist essentially of, or consist of silicone (e.g., a siliconresin). At least a portion of the encapsulant may apply a downward forceon the lens and/or on the interface material toward the light-emittingdevice. The magnitude of the downward force may be greater than 0.1 N.The light-emitting device may include, consist essentially of, orconsist of a light-emitting diode (e.g., a bare-die light-emitting diodeor light-emitting diode chip) or a laser (e.g., a bare-die laser orlaser chip). The encapsulant may include, consist essentially of, orconsist of a heat-contractive material. The encapsulant may include,consist essentially of, or consist of polytetrafluoroethylene,polyetheretherketone, a fluoropolymer such as a perfluoroalkoxy alkane,and/or epoxy (e.g., a resin of one or more of these materials). Theencapsulant may include, consist essentially of, or consist of epoxy(e.g., epoxy resin).

In another aspect, embodiments of the invention feature a method forforming an illumination device. An apparatus is provided. The apparatusincludes, consists essentially of, or consists of a light-emittingdevice configured to emit ultraviolet (UV) light, a rigid inorganic lensdisposed over the light-emitting device, an interface material disposedbetween the light-emitting device and the lens, and an encapsulant. Theencapsulant at least partially surrounds the light-emitting device andcontacts at least a portion of the lens. The lens may at least partiallyprotrude from the encapsulant. The encapsulant is partially orsubstantially fully cured. While the encapsulant is being partially orsubstantially fully cured, a downward force is applied on the lenstoward the light-emitting device (equivalently, the light-emittingdevice may be forced upward toward the lens and/or the light-emittingdevice and lens may be forced toward each other). The downward force (i)substantially prevents partial or full detachment of the lens from thelight-emitting device, and/or (ii) substantially suppresses formation ofbubbles between the light-emitting device and the lens (and/orsubstantially prevents bubbles from remaining between the light-emittingdevice and the lens).

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The apparatus may include a barrierlayer configured to substantially prevent UV light emitted by thelight-emitting device from entering the encapsulant. The barrier layermay be disposed between the light-emitting device and the encapsulant.The barrier layer may include, consist essentially of, or consist of asecond encapsulant disposed adjacent to the light-emitting device (andmay be in contact with the light-emitting device). The secondencapsulant may be opaque to UV light emitted by the light-emittingdevice. The encapsulant may be substantially transparent to UV lightemitted by the light-emitting device. The encapsulant may be opaque toUV light emitted by the light-emitting device. The encapsulant and thesecond encapsulant may include, consist essentially of, or consist ofthe same material. A penetration length of UV light within the secondencapsulant is less than or equal to 25 μm, or even less than or equalto 10 μm. A penetration length of UV light within the encapsulant may be100 μm or more.

The barrier layer may include, consist essentially of, or consist of amaterial reflective to UV light emitted by the light-emitting device.The barrier layer may include, consist essentially of, or consist ofaluminum. At least a portion of the encapsulant may be substantiallytransparent to UV light emitted by the light-emitting device. At least aportion of the encapsulant may be opaque to UV light emitted by thelight-emitting device. The UV light emitted by the light-emitting devicemay have a wavelength of 265 nm or less, or even 200 nm or less. Thelens may include, consist essentially of, or consist of quartz, fusedsilica, and/or sapphire. A top surface of the encapsulant may bedisposed above a bottom surface of the lens by at least 0.05 mm.

The magnitude of the downward force may be greater than 0.1 N. Thedownward force may be applied by contraction of at least a portion ofthe encapsulant during partial curing or substantially full curing ofthe encapsulant. The interface material may have a thickness less than 5μm. The interface material may include, consist essentially of, orconsist of silicone (e.g., silicone resin). The light-emitting devicemay include, consist essentially of, or consist of a light-emittingdiode (e.g., a bare-die light-emitting diode or light-emitting diodechip) or a laser (e.g., a bare-die laser or laser chip). The encapsulantmay include, consist essentially of, or consist of a heat-contractivematerial. The encapsulant may include, consist essentially of, orconsist of polytetrafluoroethylene, polyetheretherketone, afluoropolymer such as a perfluoroalkoxy alkane, and/or epoxy (e.g., aresin of one or more of these materials). The encapsulant may include,consist essentially of, or consist of epoxy (e.g., epoxy resin). Thedownward force may substantially suppress formation of bubbles arisingfrom decomposition of the interface material (and/or substantiallyprevent such bubbles from remaining between the light-emitting deviceand the lens).

In another aspect, embodiments of the invention feature a method foremitting ultraviolet (UV) light using a light-emitting device at leastpartially surrounded by an encapsulant. Power is supplied to thelight-emitting device, thereby causing the light-emitting device to emitUV light. While power is being supplied to the light-emitting device(and the light-emitting device is emitting UV light), UV light emittedby the light-emitting device is substantially prevented from entering(and/or deteriorating, and/or cracking, and/or penetrating more than 25μm into, or even penetrating more than 10 μm into) the encapsulant.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The penetration length of UV lightwithin the encapsulant may be 100 μm or more. UV light emitted by thelight-emitting device may be prevented from entering the encapsulant atleast in part by a barrier layer disposed between the light-emittingdevice and the encapsulant. The barrier layer may include, consistessentially of, or consist of a second encapsulant disposed adjacent tothe light-emitting device. The second encapsulant may be opaque to UVlight emitted by the light-emitting device. The encapsulant may besubstantially transparent to UV light emitted by the light-emittingdevice. The encapsulant may be substantially opaque to UV light emittedby the light-emitting device. The encapsulant and the second encapsulantmay include, consist essentially of, or consist of the same material. Apenetration length of UV light within the second encapsulant is lessthan or equal to 25 μm, or even less than or equal to 10 μm.

The barrier layer may include, consist essentially of, or consist of amaterial reflective to UV light emitted by the light-emitting device.The barrier layer may include, consist essentially of, or consist ofaluminum. At least a portion of the encapsulant may be substantiallytransparent to UV light emitted by the light-emitting device. At least aportion of the encapsulant may be opaque to UV light emitted by thelight-emitting device. The UV light emitted by the light-emitting devicemay have a wavelength of 265 nm or less, or even 200 nm or less.

A rigid inorganic lens may be disposed above the light-emitting deviceand at least partially protrude from the encapsulant. The lens mayinclude, consist essentially of, or consist of quartz, fused silica,and/or sapphire. A top surface of the encapsulant may be disposed abovea bottom surface of the lens by at least 0.05 mm. A force (e.g., adownward force) may be applied on the lens toward the light-emittingdevice (and/or a force may be applied on the light-emitting devicetoward the lens, and/or force may be applied on the lens and thelight-emitting device toward each other). At least a portion of theforce may be applied by the encapsulant. The magnitude of the force maybe greater than 0.1 N. An interface material may be disposed between thelens and the light-emitting device. The interface material may have athickness less than 5 μm. The interface material may include, consistessentially of, or consist of silicone. At least a portion of theencapsulant may apply a downward force on the lens toward thelight-emitting device. The magnitude of the downward force may begreater than 0.1 N. The light-emitting device may include, consistessentially of, or consist of a light-emitting diode (e.g., a bare-dielight-emitting diode or light-emitting diode chip) or a laser (e.g., abare-die laser or laser chip). The encapsulant may include, consistessentially of, or consist of a heat-contractive material. Theencapsulant may include, consist essentially of, or consist ofpolytetrafluoroethylene, polyetheretherketone, a fluoropolymer such as aperfluoroalkoxy alkane, and/or epoxy (e.g., a resin of one or more ofthese materials). The encapsulant may include, consist essentially of,or consist of epoxy (e.g., epoxy resin).

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, theterms “substantially” and “approximately” mean±10%, and in someembodiments, ±5%. The term “consists essentially of” means excludingother materials that contribute to function, unless otherwise definedherein. Nonetheless, such other materials may be present, collectivelyor individually, in trace amounts. Herein, the terms “radiation” and“light” are utilized interchangeably unless otherwise indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 is a cross-sectional schematic of a conventional packaged LED;

FIG. 2 is a cross-sectional schematic of a packaged UV LED in accordancewith various embodiments of the invention;

FIG. 3 is a cross-sectional schematic of a packaged UV LED in accordancewith various embodiments of the invention;

FIG. 4 is a plan-view photograph of a packaged UV LED lacking aUV-blocking barrier between the UV LED chip and a transparentencapsulant after reliability testing; and

FIG. 5 is a plan-view photograph of a packaged UV LED incorporating aUV-blocking barrier layer in accordance with various embodiments of theinvention after reliability testing.

DETAILED DESCRIPTION

FIG. 2 is a cross-sectional view of a packaged UV LED 200 in accordancewith various embodiments of the present invention. As shown, a UV LEDchip 205 is electrically and mechanically connected to the submount 110,which is itself electrically connected via one or more wire bonds 120 tothe SMD package 115. The submount 110 may include or consist essentiallyof, e.g., a ceramic material, and may have electrically conductive padsthereon to which wires 120 and electrical contacts 140 are electricallyconnected. The submount 110 may be thermally conductive in order toconduct heat away from UV LED chip 205 during operation. For example,submount 110 may include or consist essentially of aluminum nitrideand/or aluminum oxide. In other embodiments, the submount 110 mayinclude or consist essentially of one or more metals, e.g., copper, orone or more semiconductor materials, e.g., silicon. In variousembodiments, one or more of the inner surfaces (i.e., the surfacesfacing the UV LED chip 205) of the SMD package 115 are reflective to theUV light emitted by UV LED chip 205. The SMD package 115 may include,consist essentially of, or consist of, for example, one or more plasticssuch as polyphthalamide (PPA) and/or one or more ceramics such asaluminum nitride or alumina. In various embodiments, one or moresurfaces (or even the entirety) of the SMD package 115 may be coatedwith a material reflective to UV light (e.g., aluminum). For example,the inner surface of SMD package 115, i.e., the surface facing the UVLED chip 205, may be coated with aluminum formed by, e.g.,non-electrolytic plating.

The UV LED chip 205 may include an AlN substrate and, thereover, one ormore quantum wells and/or strained layers including or consistingessentially of AlN, GaN, InN, or any binary or tertiary alloy thereof.In various embodiments, UV LED 205 includes a substrate and/or devicestructure resembling those detailed in U.S. Pat. No. 7,638,346, filed onAug. 14, 2006, U.S. Pat. No. 8,080,833, filed on Apr. 21, 2010, and/orU.S. Patent Application Publication No. 2014/0264263, filed on Mar. 13,2014, the entire disclosure of each of which is incorporated byreference herein.

Rather than a conventional plastic lens, an inorganic (and typicallyrigid) lens 210 (e.g., a lens including or consisting essentially offused silica, quartz, and/or sapphire) is coupled directly to the UV LEDchip 205 via a thin layer of an interface material 215 (e.g., anorganic, UV-resistant encapsulant compound that may include or consistessentially of a silicone resin). An exemplary interface material 215that may be utilized in embodiments of the present invention is DeepUV-200 available from Schott North America, Inc. of Elmsford, N.Y. Asutilized herein, an “interface material” is a material thatsubstantially fills any air gaps between, for example, a light-emittingdevice and a lens. In some embodiments, the interface material has anindex of refraction substantially matched to at least one of thecomponents joined thereby, or an index of refraction that lies betweenthose of the components joined by the interface material. Interfacematerials may be liquid or gelatinous when applied, but may be curableto form substantially solid layers. Interface materials may or may notbe intrinsically adhesive. In various embodiments of the presentinvention, the thin layer of interface material 215 is preferably quitethin (e.g., less than 5 μm thick, or even 3 μm thick or less) tominimize or prevent deterioration thereof by the energetic UV radiationfrom the UV LED chip 205. The thickness of the interface material 215may be at least 1 μm. The inorganic lens 210 is itself resistant toUV-light-induced deterioration. This approach, which is also detailed inU.S. patent application Ser. No. 13/553,093, filed on Jul. 19, 2012(“the '093 application,” the entire disclosure of which is incorporatedby reference herein), increases the critical angle of total internalreflection through the top surface of the UV LED chip 205, whichsignificantly improves photon-extraction efficiency for the packaged UVLED 200.

In addition, an encapsulant 220 encases the UV LED chip 205 within theSMD package 115; as shown, the encapsulant 220 may not entirely cover(and may not even contact) the rigid inorganic lens 210. At least aportion of the encapsulant 220 (e.g., the portion of the encapsulant 220bordering and/or in contact with the UV LED chip 205 and/or the lens210) may be substantially opaque to the UV light emitted by the UV LEDchip 205; thus, any UV light emitted into the encapsulant 220 isconfined in an extremely shallow depth of the encapsulant 220, and theenergetic UV light does not interact with most of the encapsulant 220.Thus, the encapsulant 220 is more resistant to deterioration andcracking, and the packaged UV LED 200 exhibits greater reliability.

In preferred embodiments, the penetration length of UV light (e.g.,light having a wavelength of 265 nm or less, or even 200 nm or less) ofthe encapsulant 220, i.e., the distance within the encapsulant 220during which the intensity of the light decreases to 10% or less of theincident value, is less than 25 μm, or even less than 10 μm. (Incontrast, conventional encapsulants having penetration lengths of UVlight of more than 100 μm, may exhibit deterioration and mechanicalbreakdown after being subjected to UV light.) In various embodiments theencapsulant 220 includes or consists essentially of black epoxy resin(i.e., epoxy resin having therewithin one or more pigments to give theresin a black color). In some embodiments, the encapsulant 220 mayinclude a plurality of beads (e.g., glass beads) and/or other fillerstherewithin.

As shown in FIG. 2, a shallow portion (or “barrier layer”) 225 of theencapsulant 220 immediately surrounding the UV LED chip 205 may be abarrier to UV light, and a remaining portion 230 of the encapsulant 220farther from the UV LED chip 205 may even be transparent and/ornon-UV-resistant, as it will not be subjected to the energetic radiationfrom the UV LED chip 205. In some embodiments of the invention all ofthe encapsulant 220 is UV opaque, while in other embodiments of theinvention the remaining portion 230 of the encapsulant 220 issubstantially UV transparent. The UV-opaque barrier layer 225 may bedispensed and/or molded around the UV LED chip 205 before the remainingencapsulant 220 (i.e., portion 230) is disposed around the barrier layer225 and the UV LED chip 205. In various embodiments of the invention,with the barrier layer 225 in place, substantially all of the lightemitted from the packaged UV LED 200 is emitted through the rigid lens210 at the top of the package. The barrier layer 225 and the portion 230of the encapsulant may include, consist essentially of, or consist ofdifferent materials, or barrier layer 225 and portion 230 may becomposed of one or more of the same materials (such as epoxy, e.g.,epoxy resin), with the barrier layer 225 including one or more othercomponents (e.g., pigment) making barrier layer 225 substantially UVopaque.

In various embodiments of the present invention, the encapsulant 220(e.g., barrier layer 225) vertically overlaps the lens 210 as shown inFIG. 2. In some embodiments, the top surface of the encapsulant 220 (atleast the portion of the encapsulant immediately proximate and/or incontact with lens 210) is higher than the bottom surface of lens 210 bya distance of at least 0.02 mm, at least 0.05 mm, or even at least 0.1mm. This vertical overlap of the encapsulant 220 may advantageouslysuppress or substantially prevent formation of bubbles within theinterface material 215 (or between the interface material 215 and thelens 210 and/or the UV LED chip 205) and/or suppress or substantiallyprevent partial or full detachment of the lens 210 (and/or at least aportion of the interface material 215) from the UV LED chip 205 duringthermal curing of the encapsulant 220 and/or during UV emission (e.g.,during operation and/or during burn-in processes in manufacturing). Forexample, when the encapsulant 220 is cured by e.g., application of heat,at least a portion of the encapsulant 220 may thermally contract (dueto, e.g., heat-induced volumetric shrinkage of the encapsulant 220) andthereby apply a downward force (or “down force”) on lens 210. Theencapsulant 220 may thus include, consist essentially of, or consist ofa heat-contractive material, e.g., a resin of polytetrafluoroethylene,polyetheretherketone, a fluoropolymer such as a perfluoroalkoxy alkane,and/or epoxy.

The amount of downward force imposed on lens 210 may be, e.g., more than0.05 Newtons (N), more than 0.1 N, or even more than 0.2 N. The amountof downward force may be less than or equal to 10 N. The downward forcemay advantageously force the lens 210 toward the UV LED chip 205,maintaining contact therebetween, and thereby suppress or substantiallyprevent formation of bubbles at interface material 215. Such bubbles maybe due, at least in part, to, e.g., gas generated by decomposition ofthe interface material 215 during curing and/or during UV emission whilethe packaged UV LED 200 is in operation. For example, application ofheat to an interface material 215 including or consisting essentially ofsilicone may result in the formation of bubbles of formaldehyde gas.Furthermore, while the packaged UV LED 200 is in operation, the emittedUV light may induce a photochemical reaction that takes place in theinterface material 215, and this reaction may result in decomposition ofsilicone that may result in the formation of bubbles within theinterface material 215. The presence of the bubbles may deleteriouslyimpact the UV transparency of the interface material 215, and, if largeenough, may result in at least partial detachment of lens 210 from theUV LED chip 205.

Referring to FIG. 3, in a packaged UV LED 300, the barrier layer 225 ofencapsulant 220 may be augmented or replaced with a non-encapsulantbarrier 305 that is substantially opaque to the UV light emitted by theUV LED chip 205. For example, the non-encapsulant barrier 305 mayinclude, consist essentially of, or consist of a UV-reflective metallayer (e.g., aluminum and/or polytetrafluoroethylene (PTFE) or aderivative thereof) disposed around portions of the UV LED chip 205 thatwould otherwise contact and/or emit light into the surroundingencapsulant 220. The non-encapsulant barrier 305 may be deposited,molded, or otherwise disposed around portions of the UV LED chip 205that would otherwise contact and/or emit light into the encapsulant 220and prevents UV light from entering and deteriorating the surroundingencapsulant 220. The non-encapsulant barrier 305 may be a layer or foildeposited or wrapped around the UV LED chip 205 prior to packaging. Thenon-encapsulant barrier 305 may be attached to one or more portions thepackage (e.g., the SMD package and/or submount) prior to the UV LED chip205 being disposed within and electrically and/or mechanically connectedto one or more portions of the package. As in FIG. 2, with thenon-encapsulant barrier 305 in place, substantially all of the lightemitted from the packaged UV LED 300 is emitted through the rigid lens210 at the top of the package. Although FIG. 3 depicts the barrier layer225 of the encapsulant 220 present between the non-encapsulant barrier305 and the remaining portion 230 of the encapsulant 220, in variousembodiments of the invention the barrier layer 225 may be omitted (andthus, substantially all of the encapsulant 220 present in packaged UVLED 300 may be substantially UV transparent). In other embodiments, allor a portion of the barrier layer 225 may be disposed between the UV LEDchip 205 and the non-encapsulant barrier 305.

EXAMPLE

Reliability testing was performed on 15 packaged UV LEDs, six controldevices utilizing transparent encapsulant without a barrier layer, andnine devices utilizing a UV-opaque encapsulant barrier layer 225 inaccordance with embodiments of the present invention. The reliabilitytest was performed for a time period of 500 hours, and the devices wereexposed to 55° C. and 85% humidity under 150 mA of applied current. Ofthe six control devices, three (i.e., 50%) of the devices exhibitedcomplete failure, i.e., zero output power due to an open circuit (dueto, e.g., broken wire bonds) due to crack formation in the transparentencapsulant. FIG. 4 is a plan-view photograph of a control device 400without the barrier layer 225 or the non-encapsulant barrier 305utilized in embodiments of the present invention. As shown, a UV LEDchip 405 of the control device 400 is encased in a transparentencapsulant 410, in which cracks 415 have formed after only 255 hours ofthe reliability testing.

In contrast, all nine of the devices utilizing a UV-opaque encapsulantbarrier layer 225 in accordance with embodiments of the presentinvention maintained more than 50% of their initial output power afterthe 500 hours of reliability testing, and no cracks or mechanicalfailures were detected. FIG. 5 is a plan-view photograph of an exemplarypackaged UV LED 500 with a barrier layer in accordance with embodimentsof the present invention after the reliability testing. As shown, thepackaged UV LED 500 of FIG. 5 features a UV LED chip 505 surrounded by aUV-opaque encapsulant barrier layer 225. No cracks in the encapsulantformed for testing times of at least 500 hours.

The terms and expressions employed herein are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:
 1. A method for emitting ultraviolet (UV) lightusing a light-emitting device at least partially surrounded by anencapsulant, the method comprising: supplying power to thelight-emitting device, thereby causing the light-emitting device to emitUV light; and there during, substantially preventing UV light emitted bythe light-emitting device from entering the encapsulant, wherein: arigid inorganic lens is disposed above the light-emitting device and atleast partially protrudes over the encapsulant, and a thin interfacematerial is disposed between the lens and the light-emitting device. 2.The method of claim 1, wherein a penetration length of the encapsulantfor UV light is 100 μm or more.
 3. The method of claim 1, wherein the UVlight emitted by the light-emitting device has a wavelength of 265 nm orless.
 4. The method of claim 1, wherein the lens is a quartz, fusedsilica, or sapphire lens.
 5. The method of claim 1, wherein a topsurface of the encapsulant is disposed above a bottom surface of thelens by at least 0.05 mm.
 6. The method of claim 1, wherein theinterface material has a thickness less than 5 μm.
 7. The method ofclaim 1, wherein the interface material comprises silicone.
 8. Themethod of claim 1, wherein the light-emitting device comprises alight-emitting diode.
 9. The method of claim 1, wherein the encapsulantcomprises a heat-contractive material.
 10. The method of claim 1,wherein the encapsulant comprises a resin of at least one ofpolytetrafluoroethylene, polyetheretherketone, or perfluoroalkoxyalkane.
 11. The method of claim 1, wherein the encapsulant comprisesepoxy resin.
 12. The method of claim 1, further comprising sterilizingfluid with at least a portion of the UV light.
 13. The method of claim1, wherein the lens is disposed in contact with the encapsulant.
 14. Themethod of claim 1, wherein: the light-emitting device is disposed overand electrically coupled to a top surface of a submount; and theencapsulant does not contact a bottom surface of the submount oppositethe top surface.
 15. The method of claim 1, wherein at least a portionof the encapsulant is substantially transparent to UV light emitted bythe light-emitting device.
 16. The method of claim 1, wherein at least aportion of the encapsulant applies a downward force on the lens towardthe light-emitting device, the encapsulant comprising a heat-contractivematerial.
 17. The method of claim 16, wherein a magnitude of thedownward force is greater than 0.1 N.
 18. The method of claim 1,wherein: the light-emitting device is disposed over a submount; thesubmount is disposed over at least a portion of a solid package; and thesubmount and the package comprise materials different from that of theencapsulant.
 19. The method of claim 18, wherein the light-emittingdevice is electrically coupled to the package.
 20. The method of claim19, wherein the light-emitting device is electrically coupled to thepackage via one or more wire bonds.
 21. The method of claim 1, whereinUV light emitted by the light-emitting device is prevented from enteringthe encapsulant at least in part by a barrier layer disposed between thelight-emitting device and the encapsulant.
 22. The method of claim 21,wherein the barrier layer comprises polytetrafluoroethylene.
 23. Themethod of claim 21, wherein the barrier layer comprises a secondencapsulant disposed adjacent to the light-emitting device.
 24. Themethod of claim 23, wherein the second encapsulant is opaque to UV lightemitted by the light-emitting device.
 25. The method of claim 24,wherein the encapsulant is substantially transparent to UV light emittedby the light-emitting device.
 26. The method of claim 24, wherein apenetration length of the second encapsulant for UV light is less than25 μm.
 27. The method of claim 24, wherein a penetration length of thesecond encapsulant for UV light is less than 10 μm.
 28. The method ofclaim 24, wherein the encapsulant is opaque to UV light emitted by thelight-emitting device.
 29. The method of claim 28, wherein theencapsulant and the second encapsulant comprise the same material. 30.The method of claim 21, wherein the barrier layer comprises a materialreflective to UV light emitted by the light-emitting device.
 31. Themethod of claim 30, wherein the barrier layer comprises aluminum. 32.The method of claim 30, wherein at least a portion of the encapsulant isopaque to UV light emitted by the light-emitting device.